A pulse current is used in wide industrial fields, and many products including industrial high-voltage pulse devices, such as an electric dust collector, a plasma generator, and a laser, and medical low-frequency therapeutic devices for moving muscles with a weak pulse current, have been put into practical use. Many pulse currents for industrial equipment are characterized by a high voltage (3 to 10 kV), a low current (several milliamperes to several amperes), a high frequency (30 to 100 kHz), and a narrow pulse width (1 to 10 μs). The reason for this is that as the voltage is higher and the pulse width is narrower, higher energy can be generated momentarily.
Regarding such a pulse power supply for the purpose of generating a sharp high-voltage pulse, many patent applications have been filed. Patent Literature 1 discloses a “pulse compression technique” to cascade-connect resonant circuits, each including a capacitor and a coil, for the purpose of generating a high-voltage ultrashort pulse. Each coil used in a pulse compression circuit is a saturable reactor in which a core becomes saturated when a current at a certain level or higher flows therethrough, and the coil serves both for LC resonance and as a switching element in which a coil current suddenly increases due to magnetic saturation.
Patent Literature 2 discloses a method for stabilizing a pulse voltage. For this purpose, the method is characterized in that a charging/discharging capacitor and a plurality of inductors (coils) are connected in series and each inductor forms an LC resonant circuit including an individual capacitor, a power supply, and a switch, and timings of these multiple resonant circuits are shifted from each other, thereby stabilizing a pulse voltage. Each coil in this invention is not a saturable reactor, a resonance frequency is high, and an air-core coil is used. Thus, there is no problem of saturation of a core.
As pulse current-using equipment used in the medical field, there is a low-frequency therapeutic device. According to Patent Literature 3, muscle contraction can be caused by stimulating peripheral nerves with a pulse current having a pulse width 50 μs to 1 ms with a voltage of 100 V or lower (about several milliamperes) through an electrode attached to the skin. The low-frequency therapeutic device can cause muscle contraction with low electric power, and thus the size of the device can be very small. However, it takes time and effort to attach the electrode to the skin, and in the case of causing great muscle contraction, there is a problem that great pain is involved, since electric stimulation is an electric shock. If the electrode is buried under the skin, the problem of pain can be avoided, but there is a problem that purulence is likely to occur from a portion where an electrode wire contacts the skin.
As pulse current application medical equipment different from a low-frequency therapeutic device, there is a magnetic stimulation device. This device employs a method of stimulating nerves with an induced current generated by magnetic pulses, and has an advantage that it is unnecessary to attach an electrode to the skin. In the magnetic stimulation, a pulse current having a voltage of about 1400 V, a current of about 2000 A, and a pulse width of about 0.2 milliseconds is caused to momentarily flow through a magnetic stimulation coil to generate a strong magnetic field, and an induced current is generated in the living body by the magnetic field, thereby stimulating nerves. The electric energy of one pulse in this case is generally about 100 joules. Meanwhile, in the case of the industrial pulse power supply described above, the voltage is about 10 kV, the current is about 100 mA, the pulse width is about 1 μs, and the electric energy of one pulse is about one several hundredth of joules and is much lower than that of the magnetic stimulation pulse.
Patent Literature 4 discloses a pulse magnetic stimulation device used for therapy of urinary incontinence. This invention uses successive magnetic pulses, and thus a capacitor needs to be rapidly and repeatedly charged and discharged. The description of an electric circuit disclosed in the invention is only that: a power supply voltage is 100 to 3 kV; the capacity of the capacitor is 300 μF; and a protective resistor prevents a rush current, and, for example, problems of an increase in power consumption and heat generation of an internal element which occur with successive generation of magnetic pulses are not particularly described.